1. Field of the Invention
The present invention relates to a lamp driving circuit; and, more particularly, to a lamp driving circuit capable of enhancing efficiency and reducing a cost by being simplified by driving a plurality of lamps through a transformer of which an input terminal of a primary side and an output terminal of a secondary side face each other to satisfy safe insulation and by being manufactured on a single board.
2. Description of the Related Art
A recent trend is that an LCD (Liquid Crystal Display) is gradually widely used for a TV and a monitor with development of display technology. When comparing the LCD to a CRT (Cathode-Ray Tube) monitor, the LCD has advantages in that a longitudinal cross-section is slimmed and a flicker is reduced.
Such an LCD includes a back-light module to supply a light source without self-luminescence and the back-light module has a fluorescent lamp which is driven at a high voltage.
Meanwhile, an inverter is used to drive the fluorescent lamp of the back-light module, wherein the inverter needs a high voltage transformer which supplies a current to the lamp constituting an LCD panel by generating a high AC output voltage with a low pulse input voltage.
At this time, because the conventional transformer supplies a single lamp driving voltage through a single transformer, a plurality of transformers are needed to drive a plurality of EEFLs (External Electrode Fluorescent Lamps) or CCFLs (Cold Cathode Fluorescent Lamps) in parallel.
Further, as an LCD TV and monitor market attains maturity, a selling price drops and thus prices of parts related to the back-light module continue to drop.
Therefore, due to price pressure of the parts related to the back-light module, a constant effort to reduce the number of the parts and a cost has been made and as part of the effort, movement to develop a product which can drive many lamps through one transformer has been progressed actively.
Through the development of the product, a new transformer has been recently developed to output driving voltages for separately driving a plurality of lamps by using one transformer. At this time, a plurality of driving voltages outputted from the multi-output transformer have different amplitudes.
In case that the amplitudes of all of the driving voltages are not equal, brightness of the plurality of lamps is different, thereby reducing reliability of the back-light module. Accordingly, coils are included at output stages of the transformer to balance the driving voltages, wherein the coils can achieve current balance with an adjacent lamp by being included in each of the lamps one by one.
However, since such a lamp driving method does not secure safe insulation, a 24 Vdc conversion unit or a one-to-one transformer is added at a front stage in order to secure the safe insulation, thereby reducing efficiency and raising a cost.